Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$73.30	6.595%	$78.1341	$78.13	$78.15	$78.10
Purchase #2	$224.52	4.579%	$234.8008	$234.80	$234.80	$234.80
Purchase #3	$174.30	6.664%	$185.9154	$185.92	$185.90	$185.90
Purchase #4	$64.83	6.608%	$69.114	$69.11	$69.10	$69.10
Purchase #5	$102.90	11.429%	$114.6604	$114.66	$114.65	$114.70
Purchase #6	$102.77	9.844%	$112.8867	$112.89	$112.90	$112.90
Purchase #7	$75.96	8.711%	$82.5769	$82.58	$82.60	$82.60
7 purchase totals =	$818.58		$878.0883	$878.09	$878.10	$878.10